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And so first we need to recall from some of our previous lesson videos that the enzyme replicates, which recall is an RNA dependent RNA polymerase used by RNA viruses actually has no proof reading ability. This is one of the reasons that pandemic viruses can have such severe impact on the health of populations.ĭownload the high resolution version of the Antigenic Shift illustration.In this video, we're going to continue to talk about animal viruses and animal virus infections by specifically focusing on anti genic drift and anti genic shift. Since influenza A viruses that bear new (or novel) H or H/N combinations are perceived by immune systems as new, most people do not have pre-existing antibody protection to these novel viruses. In this process, the surface existing viral H and N proteins are not modified, but are replaced by significantly different H and Ns. In contrast to drift, pandemic viruses arise through a process known as antigenic shift. The new strain may further evolve to spread from person to person. Without undergoing genetic change, a bird strain of influenza A can jump directly from a duck or other aquatic bird to an intermediate animal host and then to humans.Without undergoing genetic change, a bird strain of influenza A can jump directly from a duck or other aquatic bird to humans.The new strain can spread from the intermediate host to humans.When the viruses infect the same cell, the genes from the bird strain mix with genes from the human strain to yield a new strain.A person passes a human strain of influenza A to the same chicken or pig.A duck or other aquatic bird passes a bird strain of influenza A to an intermediate host such as a chicken or pig.Antigenic shift can happen in three ways: The genetic change that enables a flu strain to jump from one animal species to another, including humans, is called antigenic shift. This process allows influenza viruses to change and re-infect people repeatedly through their lifetime and is the reason the influenza virus strains in vaccine must be updated each year.Īntigenic ‘shift’ occurs in HA and NA and is associated with pandemics. In essence, drift affects the influenza viruses that are already in worldwide circulation. The amount of change can be subtle or dramatic, but eventually one of the new variant strains becomes dominant, usually for a few years, until a new variant emerges and replaces it. Drift is a continuous ongoing process that results in the emergence of new strain variants. Influenza viruses can change through antigenic drift, which is a process in which mutations to the virus genome produce changes in the viral H or N. This type of genetic mutation is called “antigenic drift.” If the HA antigen changes shape, antibodies that normally would match up to it no longer can, allowing the newly mutated virus to infect the body’s cells. If the HA gene changes, so can the antigen that it encodes, causing it to change shape.Influenza virus genes, made of RNA, are more prone to mutations than genes made of DNA. If you are exposed to any of the three flu strains during the flu season, the antibodies will latch onto the virus’s HA antigens, preventing the flu virus from attaching to healthy cells and infecting them.
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